The main objective of this research is to study the mechanism of phagocytosis, both in its developmental and physiological aspects. To accomplish this we intend to extend a genetic dissection of this mechanism in the unicellular eukaryote Tetrahymena, already in progress in my laboratory. This involves obtaining a a collection of mutants individually defective in different components of this interesting mechanism and characterizing the defect in each mutant down to the molecular level if possible. A secondary objective is to begin a genetic dissection of the mechanisn of secretion or exocytosis. A promising procedure to select such mutants is now available. We expect this study to be significant in that 1. it brings an incisive experimental tool into the study of these basic cellular mechanisms. Already important insights into the relative contribution of phagocytosis to the biology of Tetrahymena have been made during the first two years of this project. The proposed renewal will hopefully contribute further insights into the developmental pathway for the constructuion of a complex cellular organelle (the oral apparatus) and the molecular machinery involved in the membrane dynamics of phago- and exoctyosis. Finally, concepts and approaches developed here may find application in basic and clinical medicine, in view of the vital roles certainly placed by both of these mechanisms in the healthy functioning of our body.